How to find parents' genotypes from progeny phenotype frequencies?

In summary, from the given information of phenotypes and their frequencies, we can determine the parental and recombinant phenotypes. To know if the genes are linked, we can calculate the recombination frequencies and if they are less than 0.5, then the genes are linked. The possible genotypes of the parents are a+ b+ c+/a+ b+ c- and a- b- c+/a- b- c-.
Question: 8 phenotypes were observed as a result of a trihybrid cross. The frequencies of the phenotypes are

a+ b+ c- = 570
a- b- c+ = 545
a+ b- c+ = 17
a- b+ c- = 20
a+ b- c- = 140
a- b+ c+ = 128
a+ b+ c+ = 65
a- b- c- = 61

No other information is given. It is not even specified if it is a testcross. How to know if the genes were linked? Also, what are the possible genotypes of the parents?

My attempt - The phenotypes with the two largest frequencies represent parental classes. Thus a+ b+ c- and a- b- c+ are parental recombinant phenotypes.
The phenotypes a+ b- c+ and a- b+ c- are double recombinant phenotypes as these have the smallest frequencies. The other 4 are single recombinant phenotypes.
But I do not know how to proceed from here.

Suppose I calculate the % of all the recombinant (single and double) phenotypes and find it to be less than 50%, can I conclude that the genes were linked?

Answer: To determine if genes are linked, you need to look at the recombination frequencies. Calculate the recombination frequency between each pair of genes by dividing the number of double recombinant phenotypes (a+ b- c+ and a- b+ c-) by the total number of offspring. If the recombination frequency is less than 0.5 for any pair of genes, then the genes are linked. The possible genotypes of the parents would be a+ b+ c+/a+ b+ c- and a- b- c+/a- b- c-.

1. How do you determine the genotype of parents from the phenotype frequencies of their offspring?

The process of determining the genotype of parents from the phenotype frequencies of their offspring involves using the principles of Mendelian genetics. This includes understanding the laws of segregation and independent assortment, as well as identifying the dominant and recessive traits. By analyzing the ratio of phenotypes in the offspring, one can determine the possible genotypes of the parents.

2. What information do you need to know in order to find the parents' genotypes from progeny phenotype frequencies?

In order to determine the parents' genotypes, you will need to know the phenotype frequencies of their offspring, as well as the dominant and recessive traits for the specific gene or trait being studied. It is also helpful to know the principles of Mendelian genetics and the expected ratios of phenotypes based on different genotypes.

3. Can you use the phenotype frequencies of more than one offspring to determine the parents' genotypes?

Yes, using the phenotype frequencies of multiple offspring can provide a more accurate determination of the parents' genotypes. This is because a larger sample size reduces the potential for chance occurrences and allows for a more reliable analysis of the phenotypic ratios.

4. What are some limitations of determining parents' genotypes from progeny phenotype frequencies?

There are a few limitations to this method, such as the possibility of incomplete dominance or co-dominance, which can affect the phenotypic ratios. Additionally, the presence of genetic modifiers or environmental factors can also influence the phenotype frequencies and make it more difficult to accurately determine the parents' genotypes.

5. Can the parents' genotypes be determined with 100% certainty using this method?

While the principles of Mendelian genetics can provide a strong basis for determining the parents' genotypes from progeny phenotype frequencies, it is not always possible to determine them with absolute certainty. Other factors, such as genetic modifiers or environmental influences, can affect the results and make it challenging to determine the exact genotypes of the parents.

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